A pilot signal (or reference signal) is commonly used for communication systems to enable a receiver to perform a number of critical functions, including but not limited to, the acquisition and tracking of timing and frequency synchronization, the estimation and tracking of desired channels for subsequent demodulation and decoding of information data, the estimation and monitoring of characteristics of other channels for handoff, interference suppression, etc. Several pilot schemes can be utilized by communication systems and typically comprise the transmission of a known sequence at known time intervals. A receiver, knowing the sequence only or knowing the sequence and time interval in advance, utilizes this information to perform the abovementioned functions.
For the uplink of future broadband systems, single-carrier based approaches with orthogonal frequency division are of interest. These approaches, particularly Interleaved Frequency Division Multiple Access (IFDMA) and its frequency-domain related variant known as DFT-Spread-OFDM (DFT-SOFDM), are attractive because of their low peak-to-average power ratio (PAPR), frequency domain orthogonality between users, and low-complexity frequency domain equalization.
In order to retain the low PAPR property of IFDMA/DFT-SOFDM, only a single IFDMA code should be transmitted by each user. This leads to restrictions on the pilot symbol format. In particular, a time division multiplexed (TDM) pilot block should be used, where data and pilots of a particular user are not mixed within the same IFDMA block. This allows the low PAPR property to be preserved and also enables the pilot to remain orthogonal from the data in multi-path channels, since there is conventionally a cyclic prefix between blocks. An example is shown in FIG. 1, where an IFDMA pilot block and subsequent IFDMA data blocks for a transmission frame or burst are shown.
While the TDM pilot approach is attractive, there are a limited number of separable or orthogonal pilot signals available for use by different transmitters in a system. Therefore a need exists for a method and apparatus for pilot signal transmission that increases the number of separable pilot signals.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.